Systemic lupus erythematosus is a disease of unknown etiology, but the glomerulonephritis and other manifestations of this illness are caused by antigen-antibody complexes that have been found at the glomerular basement membrane. This disease is variable from patient to patient in its severity; some patients have no renal disease, others have a mild glomerulonephritis and some patients die from progressive and relentless disease. The reasons for this variability are not known. In the proposed work experimental animals will be used to elucidate the reasons for variations in immune complex glomerulonephritis. The physical size of the immune complexes and the affinity of antibodies will be studied in relation to the localization of immune complexes in the glomeruli on the ultrastructural level with immuno-electron microscopy. The relationships between the dose of immune complexes and kidney damage will be evaluated. The information from studies with experimental animals will be applied to investigation of lupus glomerulonephritis. On the ultrastructural level several antigens will be localized in glomeruli. The circulating antibodies and antigens will be quantified. This information will be related to the severity of the disease. The information obtained from these studies should open new approaches to treatment of systemic lupus erythematosus.